1. Field of the Invention
The present invention relates to an electron emission display and a driving method thereof, and more particular to an electron emission display and a driving method thereof, which adjust a brightness differently according to a brightness of a frame in order to reduce power consumption and prevent a gradual failure from occurring.
2. Discussion of the Related Art
Lightweight and thin flat panel displays have been used as either a display device for a portable information terminal such as a personal computer, a portable telephone, and a personal digital assistant (PDA) or a monitor of all kinds for information devices. A liquid crystal display (LCD) using a liquid crystal panel, an organic light emitting display using an organic light emitting diode, and a plasma display panel (PDP) using a plasma panel are examples of flat panel displays.
A flat panel display is classified into active matrix type displays and passive matrix type displays according to its construction, as well as a memory drive type and a non-memory drive type according to a light emitting theory. In general, the active matrix type can correspond to the memory drive type, and the passive matrix type can correspond to the non-memory drive type. The active matrix type and memory drive type displays emit light in frames. In contrast to this, the passive matrix type and non-memory drive type displays emit light in lines.
In commonly used flat panel displays, TFT-LCD (Thin Film Transistor Liquid Crystal Display) is an active matrix type, and a newly developed organic light emitting diode (OLED) is also an active matrix type. In contrast to this, an electron emission display is a passive matrix type display device. Unlike flat panel displays, the electron emission display is a non-memory drive type and uses a line scan type that emits light only when a selected line among horizontal lines is selected while sequentially selecting the horizontal lines. That is, the electron emission display drives to have a constant duty ratio.
An electron emission display includes a pixel portion, a data driver, a scan driver, a timing controller, and a power supply section. The pixel portion includes pixels formed at intersecting parts of cathode electrodes C1, C2 . . . Cn and gate electrodes G1, G2 . . . Gn. In the pixels, electrons emitted by the cathode electrodes collide with the anode electrodes to emit light of fluorescent substances, thus representing a gray scale of an image. The represented gray scale of an image changes according to a value of an input digital image signal. In general, in order to adjust the gray scale expressed according to the value of a digital image signal, a Pulse Width Modulation mode or a Pulse Amplitude Modulation mode can be used.
The data driver is coupled with the cathode electrodes C1, C2 . . . Cn, and generates and transfers a data signal to the pixel portion, so that the pixel portion emits light corresponding to the received data signal. The scan driver is coupled with the gate electrodes G1, G2 . . . Gn, and generates and transfers a scan signal to the pixel portion, the pixel portion sequentially emits light during a predetermined time period in horizontal line units and in a line scan manner. This causes a total screen to be displayed, thus reducing the costs of circuit and power consumption.
The timing controller transfers a data driver control signal and a scan driver control signal to the data driver and the scan driver in order to control operations of the data driver and the scan driver, respectively. The power supply section supplies power to the pixel portion, the data driver, the scan driver, and the timing controller, so that the pixel portion, the data driver, the scan driver, and the timing controller can operate.
The electron emission display having the construction as mentioned above expresses a gray scale according to brightness data regardless of total frame data. Consequently, in order to express more brightness, more current flows through the pixel portion. In order to express less brightness, less current flows through the pixel portion. In this scenario, when more current flows through the pixel portion to express a higher brightness, a larger load burdens the power supply section. This results in the power supply section having to put out a high output. Because a person can more easily sense a brightness change in dark image than a brightness change in a bright image, the brightness change amount of the bright image should be increased. Therefore, what is needed is an electron emission display and a method to adjust brightness so that the power supply is not subject to excessive load while providing a better image.